It is often desirable or advisable to modify the suspension of an automobile, either for esthetic reasons or to improve the driving and road handling characteristics of the automobile. Likewise, modifying the body of an auto often requires that the suspension be modified to accommodate the new body features, and the new weight distribution caused by the body modifications. In prior art suspension systems which commonly employ leaf springs or coil springs, it is a relatively simple matter to substitute new springs, or new shock absorbers, to change the suspension system, in addition to changing the size and length of other suspension parts, by substitution, modification, and the like.
However, prior art suspension systems which employ torsion bar spring assemblies have presented unique obstacles to modification that have defied simple or cost-effective solutions. A typical torsion bar spring suspension, such as that provided as original equipment in Volkswagen automobiles and vans, includes at least one torsion spring composed of a plurality of spring leaves bundled together. The torsion spring is received within a tubular beam housing, and an internal mounting block secured in a medial portion of the beam housing rigidly secures the medial portion of the spring to the housing. The free ends of the torsion spring are joined to trailing arms or the like which extend to the respective wheels, so that deflection of the wheel caused by the weight of the vehicle and road shock is resiliently resisted by torsion of the spring.
In order to modify the torsion spring suspension assembly; e.g., to reduce clearance to the roadway or increase the spring force and "tighten" the ride, it is necessary to rotate the torsion spring(s) to adjust the nominal angle of the trailing arms which control the wheel spacing with respect to the vehicle body. This task has proved to be a formidable problem. The internal mounting block is firmly anchored in the beam housing by a set screw and portions of the beam housing wall peened into recesses in the mounting block, specifically for the purpose of preventing rotation of the torsion spring.
The torsion bar assembly can be removed from the internal mounting block and withdrawn from one end of the beam housing, but the mounting block remains within and requires that the torsion bar be reinserted at exactly the same angle. One approach to rotating the torsion spring involves cutting the beam housing circumferentially about either side of the internal mounting block, rotating the cutout section and the torsion spring that is still rigidly affixed thereto, and then rewelding and joining the cutout section in its new position. This restructuring of the beam housing can weaken the beam housing and lead to failure of the suspension, either immediately, or, more insidiously, after a period of normal use. Furthermore, in suspensions that employ two torsion springs in two beam housings, the upper beam is more easily modified in this way, and the lower beam is usually unchanged. As a result, the lower spring must bear a greater amount of torsional rotation and support a greater proportion of the vehicle weight, leading to uneven and excesive wear on the ball joints, trailing arms, and other related components.
In the two beam, two torsion spring suspension, if the lower beam is modified, there are further complications and problems. The lower beam secures the idler arm support box of the steering mechanism. First, it must also be cut off to achieve the desired rotation of the spring, and then rewelded in a new position angularly offset from its original placement. It is likely that the beam and the idler arm support box and its junction to the lower beam is weakened; if this support box becomes partially or totally detached, abrupt loss of directional control of the vehicle will result. The potential for catastrophic accident is obvious.
It should also be noted that the repositioned torsions springs are again secured in a fixed angular relationship relating to the respective beam housing, and there is no adjustment possible in the trailing arm angle and the height of the wheels with respect to the vehicle. Thus the process of cutout and rewelding must be performed perfectly, as there is no possibility of revising or readjusting the outcome.
An adjustable torsion bar suspension known in the prior art was produced in prototype form for the Porsche automobile. It featured a rotatable central mounting bushing, and a set screw extending from the bushing through a slot in the beam housing. However, the arrangement for securing the set screw to maintain the torsion beam angle included two lock nuts disposed atop a plate which engaged a toothed set plate. This construction was unstable and weak, and the height of the two lock nuts combined with the plate and set plate made this device too large to fit into the crowded area of the automobile suspension. Furthermore, this arrangement did not address the problem of altering the standard torsion bar assembly which is fixed in place by peened areas of the beam housing engaging depressions in the central mounting block.
Another approach to lowering the vehicle body (reducing road clearance) is to remove one or more of the leaves from the torsion spring bundle. This results in a reduced spring constant for the torsion springs, so that the vehicle weight caused greater flexure of the springs and allows the body to assume a lower nominal road clearance. However, the lower spring constant also provides a softer ride, so that road shock drives the wheels to undergo excessive movement. The wheels are thus liable to impact and interfere with the vehicle body.
It is clear that there is an unmet need in the prior art for an apparatus and approach to revise and modify the typical torsion bar suspension in a manner that is safe, economical, practical, and adjustable.